Venous thrombosis and thromboembolism remain a national health problem, occurring with an annual incidence of 250,000 cases and resulting in 300,00 to 600,00 hospitalizations and 50,000 deaths per year. The incidence has not changed over the past 30 years. Venous thrombosis leads to chronic venous insufficiency with as many as 500,000 patients affected with skin ulceration from venous insufficiency and 6 to 7 million patients with skin stasis changes. Our ongoing hypothesis is that chronic venous insufficiency results from an interplay between thrombosis and inflammation (initiated by thrombosis), and that the inflammatory response amplifies thrombosis. We have demonstrated the following: 1) the inflammatory response initially involves neutrophil extravasation into the vein wall followed by monocyte emigration; 2) signaling cytokines in the vein wall such as tumor necrosis factor (TNF) are important for this leukocyte movement; 3) inhibition of pro-inflammatory cytokines will lessen the inflammatory response. Additionally, we have also noted the presence of the anti-inflammatory cytokine interleukin-10 (IL-10) in high quantity in the vein wall in response to venous thrombosis. Our new hypothesis is that venous thrombosis induced inflammation involves an imbalance between anti- inflammatory and pro-inflammatory cytokines favoring inflammatory and thrombotic amplification. In this proposal, we will investigate the interplay between the thrombus and vein wall once clot has formed. We will: 1) Evaluate the magnitude of expression, time course and cellular sources of the anti-inflammatory cytokine IL-10 and its receptor during venous thrombosis correlated to pro-inflammatory cytokines and determine their relationship to the thrombotic and inflammatory response without and with IL-10 neutralization; 2) Define the specific relationship between IL-10 and TNF in vitro and determine the interplay between these anti-inflammatory and pro-inflammatory cytokines in isolated monocytes derived from blood and both vein wall and thrombus during venous thrombosis; 3) Determine the effect of IL-10 over expression on the inflammatory and thrombotic response during venous thrombosis using both localized transient transfection of the IL-10 gene into the vein wall and systemic administration of rIL-10. This investigation should further our understanding of the balance between anti-inflammatory and pro-inflammatory activities of the vein wall produced by venous thrombosis, the manner in which these activities affect thrombus amplification and suggest therapeutic options to lessen inflammation and thrombosis.